Reception of frequency modulated waves



May 30, 1944. o. IRSLINGER RECEPTIQN 0F FREQUENCY MODULATED WAVES Filed Jul 17, 1941 4 Sheets-Sheet 1 Fig.1

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RECEPTION 0F FREQUENCY MODULATED WAVES Filed July 17. 1941 4 Sheet-Sheet s lnvenivl': arm as; fives/i;

" QM R o. IRSLINGER 2,349,966

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E Y W M m m 0 Patented May 30, 1944 NITED srArEs PATENT orrrcr:

RECEP'iIbN MODULATED Otto vested in the Alien Property Custodian Application July 17, 1941, Serial No. 402,827

vIn Germany July 18, 1940 2'Claims. (g1. 250- 20) The invention comprisesdevices for the reception of frequency modulated waves. It is known that with those waves not the amplitude but the frequency varies rhythmically in accordance- The amplitudeof' with modulating potentials. frequency modulation isdependent on the par ticular signal strength.

, For receiving it is necessary to. converttthe frequency modulated waves correctly into variations of amplitude. Formerly one has used special converters. Suchaconverter can be, for example, an inductivity having a linear frequency characteristic as long as one; keeps suf-' ficiently beneath or above the resonance ire-- Another object of the invention is keeping ex-' actly the frequency at v a constant value, for

example, the intermediate frequency appearing in superheterodyne receivers.

A still further object of the/invention is the linear amplification of frequency modulated waves.

The invention is especially useful for ultra short wave devices of a wave length of less than 1 metre but it is' not limited to those wave lengths.

The fundamental feature of the receiving device is the variation of the local oscillator. in regard to its frequency in such Way that a com stant intermediate frequency is the result. The variations of frequency in regard to the calculated value are to be used as a control quan tity. The control quantity is retroactive upon the oscillator in such manner, that the intermediate frequency is kept as exactly as possible at its calculated value. The control quantity varies rhythmically with the frequency modulation of the received waves and can be made audible in a telephone or the like. Thus a special converter is not necessary because the control quantity itself shows exactlythe variations of amplitude according to the variations of frequency; For

Furthermore the limiting device for modulated vibrations purpose one needs a frequency bridge device which produces the control quantity. In this case there must be a remaining deviation of the calculated value which is dependent on the control steepness so that an exact controlling to deviation zero is not possible (static regulation); Since this condition may exist at image fre-- quencies the regulation is active. in the reverse sense as there are no negative frequencies. Hence,

it is necessary that the apparatus employed actually .diminish the deviation.

According to a preferred embodiment of invention these disadvantages can be avoided by adjusting the oscillator in anotherway. For this purpose a quantity is used being proportional to the phase. difference, between the intermediate frequency and a. constant auxiliary oscillator.

This desired result is obtained from the phase relations which exist in an oscillatory circuit.

The latter is tuned to the intermediate frequency we of the carrier wave. If the frequency of the received wavevaries the phase relations between current and voltage in the oscillatory circuit vary too and the oscillatory circuit is highly sensitive for such variations.

The objects of the invention will be understood best from the following specification in connection with the drawings in which:

Fig. 1 shows the principle circuit of the re} ceiver,

Fig. 2 is a graphical representation of the frequency relations,

"Fig. 3 shows the phase bridge device and I Figs. 4a and 41) show the vector diagram of the bridge device,

Fig. 5 shows a modification of the phase bridge device of Fig. 3.

Figs. 6 and 7 represent characteristics curves of the mode of operation of the receiver,

Figs. 8 and 9 show in principle the regulation of the oscillator tube, Fig. 10 is a graphical representation of the frequency-variations,' 1

Fig. 11 shows thediagram of connections of i The principle of theinvention is schemati ifi The received frequency are superheterodyned with the vibrations of a local oscillator. The

represented in Fig. 1.

resulting intermediate frequency is indicated in Fig. 1 with B and it'is to be kept at a constant value as far as possible. Furthermore'the aux- Jiliary transmitter A is provided having an exact the f the deviation zero is possible as the control quantity does not become smaller. with'decreas' Furthermore the w ing difference of frequency. above described difficulties in regard to the image frequencies fall off, as there exist of oourseno negative frequencies but a negativephase The coordination of the control quantity to the phase difference therefore has but one meaning.

The regulation regarding this occurs as follows: Both frequencies a and b being different at the beginning let it' be known that they possess a gradually increasing phase difference 1 This permanently increasing phase difference produces in the phase bridge device a control quantity being retroactive to the intermediate frequency 1) in such way that the phase difference is diminished. The frequency 1) will be adjusted regarding its phase to frequency a. In the final state of the regulation a fixed phase difference is reached being just large enough to keep the control quantity u to a constant value. Contrary to the above described regulation in the final state no deviation from the calculated In the state of value of frequency is necessary. equilibrium both frequencies have exactly the same value and differ only by a constant phase difference (astatic regulation).

For this reason the phase shifting at the oscillatory circuit between current and voltage is to be transformed into corresponding direct currents. The principal. diagram of connections of such a phase converter is shown in Fig. 3. With T1 and Tz'two-transformers are shown being fed by the voltages U1 and U2. The secondary winding of transformer T1 is connected with the anodes of a duo-diode D whilst the secondary winding of T2 is connected-to the cathode of the diode D and to the middle tap of secondary winding of transformer T1. The ratio of the two transformers T1 and T2 is proportional to 2:1. If the two voltages U1 and U2 have a phase difference of, for example, 90 one gets the vector diagram according to Fig. 4a. The angle of phase 1 is 90. The voltages U and Us along the spaces between cathode and anodes of the duo-diode have the same amplitude. The corresponding currents Jo and J1 have therefore also the same value. If the phase has not the value of 90 other relations result as shown, for example, in Fig. 4b. The voltage along both spaces of the duo-diode now are different and therefore are causing different currents. In the case U1=2 and Uz=1 the voltage at the duo-diode are? U =2 sin 2 and -by transmitter A (standard frequency) whilst the voltage U2 will be produced by the intermediate frequency transmitter. The differences of phases between both voltages produce in the duodiode the voltages U0 and U11 as is shown in Fig.

4. The control quantity can be gained at the points P and Q (Fig. 5) and is proportional to the currents Jo and J11. The characteristic curve of the diode can be assumed linear and therefore one gets for the control quantity:

7 Now it is assumed that the standard oscillator A For converting the currents again into voltages 7 5' quency of oscillator B by the control vibrates with the constant frequency a. It is now the question in which manner the regulation of the intermediate frequency 1) is dependent on time. For the oscillations of the transmitter I A and B one gets (see Fig. 2):

It is remarkable that w is not constant but a.

function of time t itself.

The difference of phase between these two oscillations is:

go= f(Dw) dt+po the control quantity one gets:

1L=K1'C0s f(Dw )dt|p0] It is always possible that the regulation of freis linear. One thus can write:

I I w=K2"Ll,

In substituting into this equation the value of the control quantity u one gets the equation for w:

where K=K1-K2, which also may be called as resulting'steepness. This equation leads to' a differential equation, which becomes finally:

2 2.10 cosm The starting conditions being t=-0 and w l). cos" e50, one gets the constant C2 The relations as above are shown'in Figs. 6 and quantity u 7. The constantCis m at o -"0, it has the valve 1 at p='90 and the value 0 at po=180. .In Fig. 7 the quantity or is shown in dependence on time)? and quantity C: and at the same time the term :r=Dt+C' is chosen. The asymptotical course of the curve shows that at all values of be a cor-- rectradjustment oftransmitter B takes plaee. In other words this means that the .receiver sis properly controlled for all differences of phases in the starting point. Starting oscillations are decreasing quickly; oscillations of regulations do not occur. vibrations have the phase difference zero against each other the oscillator .B will be at once oscillating in the correct frequency.

In Fig. 8 a principal diagram of connections of the receiver according to the invention is shown. The oscillations coming from the am,

for there takes place'aregulation o f'oscillator-O in such manner thata constant intermediate frequency results. The standard oscillator A leads its constant frequency to the other branch off (the phase bridgekdevice; The control 'voltage,pro-- duced in the bridge device is retroactive to the oscillator O and makes the adjustment off-the latter. Besides thisthe current for the telephone or the like is gained from the control quantity and there might also be provided between same a low frequency amplifier'NF. In this embodiment the oscillator is a brake field generator and the control quantity gained in the bridge device Ph acts on the voltageof the brake field electrode. The negative voltage of the brake field electrode is given by battery Q.

The shown phase bridge'device corresponds to that, of Fig..5. The windingsof the transformer being circuited into the anode leads ,of duodiode. are connected through resistances and condensers in parallel-connection for. reaching a favorable receiving of the diode voltagcs.

Fig. 9 shows acomplete embodiment ventionirr which a brake field tube is' controll df The voltage which is to be controlled inrespe'ct to its frequency is led at I to an amplifier comprising the shield grid tube 2. The amplified voltage runs to the oscillatory circuit .whicl 1 transforms the variations-of frequency into phase shiftings. After further amplification in transformer To and tube 3 the voltage is led tq-tr ansformer T2 corresponding to transformer'Tz in Fig. 5. One part of the controllable voltage I -wi1lbe divided before or behind the first amplifier tube 2, for example, at 5 and will ,b'eled to'-trans former T1, being subdivided into two parts T1 and T1" as shown in Fig- 5 and which secondary winding is connected with the anodes of the duo- If especiallyin the beginning-both the.

diodeD. These two parts of windings are short circuited for high frequency by the condensers (h,

and C2. The control voltage willbeatapped at the resistance R0 and Rn, for example, insuch manner that the brake field electrode of tube 1 is The battery for the" If the voltage I has its calculated valuei'n respect to the frequency no difference of phase results at the oscillatory circuit 5. The difference of the device is therefore zero. If on'the contrary the frequency Voltages in-the phase bridge of voltage I varies, phase--difierences at the oscillatory circuit will appear in regard to the voltage tapped at 5 and the hereby caused voltages in the bridge device effect variations of the brake field voltage of tube 1. The latter serves as oscillator and effects the adjusting of'frequency of the intermediate frequency'produced in the diode a V The advantages of the invention are such that several parts of the superheterodyne receiver especially the limiting device and th converter, can be left off. As a result of this one reaches an small band of frequency. By this the noise is: lowered for the latter is proportional to the root of the width of band of frequency.

In regard to the amplifying of frequency modulated waves certain considerations are necessary.

It is well known that at the amplifying of :amplitude modulated waves nonlinear distortions exist being caused by the curved course of the Besides the course characteristics of the tubes. of phase between current and voltage in dependence of the frequency is less essential. For frenonlinear distortions.

The following description will show by calculation the .bad influence of the course of phase;

and finally an arrangement is shown which will avoid or diminish the distortions in aperiodic amplifiers.

With frequency modulated waves the frequency varies according to the rhythm of modulation.

The carrier ,or middle frequencyis signed we and (momentary frequency). That is:

In Fig. 10 the frequency w is drawn as ordinate against the time t as abscissa. The frequency w.

varies to both sides about the value wo.

It maybe assumed that the waves may be modulated sinusoidally with the modulating frequencyn; Then the oscillation can be expressed by, the 1 following equation; 7

in'g phase pad) in respect to the time t:

w ere stomp o sin of. The quantity b o is called amplitude of frequency (see Fig. 10).

In the amplifier now phase displacements are existing, beihgIdependent on the momentary value of he. I Theoscillation at the output of the ampli- Thus one gets a lesser disposition for.

V .sin (wofl bcos (if) :A. sinlpdtll :1 From 'this one gets the frequency in differentiat- In this case a (we) is the phase displacement being dependenton the frequency. In regard to the frequency behindlthe amplifier follows that d*" qu=%q= w +b.ll.sin Dbl-E; v 5

d d e I I .M=w +b.SZ.-s1ni2t+ag:.7; The term I. m

dt' meansgnowi 2 i I 15. dz bQ cos lit 7 In'substituting this' value in we one gets: 7 do;

c n w -i-bil s n M l- 379 co izt V g I do; w =w +b.Q.[S1I1 S2t+ 9 m Whilst how the quency modulation before the amplifier. is: I I l mot) .ol. sin or behind the amplifier it is as follows:

Inthis case only Variations of the amplitude take place effecting a lifting of the higher frequencies according to the term 2 /1+,o M I I Therefore only linear distortions occur.

In general the term a v n is however a function of time for it is possible to develop'we into a Fourier-series. Therefore it, is: V v 7 mm. (t) 'b nEsin Qt+i2 cosnt Thus here are acting the products of sin'and cos members i. e, wm. (t) is nonlinear distorted and therefore also at'th'e converter, which transforms the frequency modulations into amplitude variations nonlinear distortions are received.

For avoiding thesedistortions the amplifier can be constructed of several single parts shown. in Fig. 11. Each part contains a tube I having be- 6 tween anode and'cathode the unavoidable capacity C. Furthermore the inductance L and the ohmic resistance R is connected in series connection between anode and cathode tube l. The input of the amplifier isnamed E and the output A. I To A one or more other amplifiers are connected. Now it is the question whether the quantities R, L, C can be chosen in such way that the demanded reception without any distortion can be reached.

" phase is in countersense.

expected that in series connection of two such (where is the root of -1).

For simplifying the calculation the following abbreviations may be chosen:

From there follows:

and

' w LC=k 13 With these abbreviations one can write:

'1 kw ms I 1 From this follows for the phase angle a tyd =k x (1 -k) a:

In the following the two cases may be considered:

These curves are shown in Fig. 12. From were it is to be seen thatinboth curves the course of It is therefore to be amplifiers a course of phase results having lesser phase variations than each single amplifier. For abbreviationthe following terms are chosen:

sary. For 'k=0 the abscissa is i=0: and for Ic ';i the abscissa is 512:1.

The displacement of the scale may be given by the constant in the following manner:

e=T.T

The value of the constant 1' shall be given by the condition that at the intersection of both curves (r=,=x.) the ordinate zo=z1= is half the value of 20 at the point e=0. In this case the value of the resultant curve at the intersection point will be the same as the beginning where the value of curve 2 (corresponding to k=1) is zero, as is shown in Fig. 12. In this case it is expected that the resultant deviation differs only little from these values. The mathematical expressions are:

me ME) =%a( From these equations one can gain '1 and i. The result is:

The last equation expresses: for getting no variations in the course of phase up to a distinctly limiting frequency on; in the range zr=0 to a:=0.56, two amplifiers with the predetermined tube capacities Co and Cl have to be connected in series. The first amplifier has only the resistance R0 for Lo=0 as k=0. The second amplifier has the series connection of the resistance R1 and the inductivity 1= 1 C1 as 79:1.

The quantities To and T1 are connected to each other over the constant 1=1.79. It is To=1-.T1.

In considering To=RoCo one gets the three equations:

wgc0R0=0-56 1.79 C1R 1=CoRo L1=R1 Ci In these three equations except the predetermined quantities 013', C0 and C1 the unknown quantities R0, R1 and L1 are stated which can be determined in a manner having but one meaning.

What I claim is:

1. In a heterodyne type receiver for receiving ultra high frequency modulated signals, a circuit for receiving said signals, a local oscillator connected to said circuit for producing an intermediate frequency in conjunction with said frequency modulated signals, a fixed reference oscillator, control means comprising a phase bridge and voltage regulating means connected between the phase bridge and said local oscillator for regulating said local oscillator to maintain said intermediate frequency substantially constant, said phase bridge comprising, a double diode having cathode means and two anodes, and two transformer means each of which has a primary winding and a secondary winding, one of said transformer means having its primary winding connected to said fixed reference oscillator and having its secondary winding divided into two equal sections with the opposite ends of the secondary winding connected respectively to the two anodes of said double diode, the other of said transformers having its primary winding connected to said signal receiving circuit to receive the intermediate frequency and having its secondary winding connected between said cathode means and the juncture of the two sections of the secondary winding of the first-named transformer, and audio frequency responsive means connected to said voltage regulating means.

2. In a heterodyne receiver for receiving ultra high frequency modulated signals, a double diode having two anodes and cathode means to cooperate with the two anodes, means connecting each of the anodes with the cathode means, a circuit for receiving said signals, a local oscillator connected to said circuit for producing an intermediate frequency in conjunction with said frequency modulated signals, transformer means having a primary winding connected to said circuit to receive said intermediate frequency and a secondary winding in said connecting means with one terminal connected directly to said cathode means whereby the signal is impressed in series with said cathode means, a fixed reference oscillator, a divided transformer means having primary winding means connected to said fixed reference oscillator and having two equal secondary winding portions connected together in said connecting means and respectively associated with said two anodes with each anode connected directly to one terminal of the secondary winding portion associated therewith, the juncture between said secondary winding portions being connected to the first-named secondary winding on the side opposite said cathode means, whereby said double diode and said transformer means form a phase bridge, a second circuit connected between said phase bridge and said local oscillator for regulating the latter to maintain said intermediate frequency substantially constant, and audio frequency responsive means connected to said second circuit.

OTTO IRSLINGER. 

